From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: Dave Airlie <airlied@gmail.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
LKML <linux-kernel@vger.kernel.org>,
DRI Development <dri-devel@lists.freedesktop.org>,
"moderated list:DMA BUFFER SHARING FRAMEWORK"
<linaro-mm-sig@lists.linaro.org>, Olof Johansson <olof@lixom.net>,
Daniel Vetter <daniel.vetter@intel.com>,
Sumit Semwal <sumit.semwal@linaro.org>,
Linux Media Mailing List <linux-media@vger.kernel.org>
Subject: Re: [Intel-gfx] [PATCH 3/3] misc/habalabs: don't set default fence_ops->wait
Date: Tue, 12 May 2020 08:12:11 +0200 [thread overview]
Message-ID: <CAKMK7uF=SzeEBtZ9xH+jPzeML4V0QQuwBnPVw+OL+MUgTaaLzQ@mail.gmail.com> (raw)
In-Reply-To: <CAPM=9tyukFdDiM6-Mxd+ouXCt9Z4t6LRZwxq7DGoX9drrHnMdQ@mail.gmail.com>
On Tue, May 12, 2020 at 4:14 AM Dave Airlie <airlied@gmail.com> wrote:
>
> On Mon, 11 May 2020 at 19:37, Oded Gabbay <oded.gabbay@gmail.com> wrote:
> >
> > On Mon, May 11, 2020 at 12:11 PM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> > >
> > > It's the default.
> > Thanks for catching that.
> >
> > >
> > > Also so much for "we're not going to tell the graphics people how to
> > > review their code", dma_fence is a pretty core piece of gpu driver
> > > infrastructure. And it's very much uapi relevant, including piles of
> > > corresponding userspace protocols and libraries for how to pass these
> > > around.
> > >
> > > Would be great if habanalabs would not use this (from a quick look
> > > it's not needed at all), since open source the userspace and playing
> > > by the usual rules isn't on the table. If that's not possible (because
> > > it's actually using the uapi part of dma_fence to interact with gpu
> > > drivers) then we have exactly what everyone promised we'd want to
> > > avoid.
> >
> > We don't use the uapi parts, we currently only using the fencing and
> > signaling ability of this module inside our kernel code. But maybe I
> > didn't understand what you request. You want us *not* to use this
> > well-written piece of kernel code because it is only used by graphics
> > drivers ?
> > I'm sorry but I don't get this argument, if this is indeed what you meant.
>
> We would rather drivers using a feature that has requirements on
> correct userspace implementations of the feature have a userspace that
> is open source and auditable.
>
> Fencing is tricky, cross-device fencing is really tricky, and having
> the ability for a closed userspace component to mess up other people's
> drivers, think i915 shared with closed habana userspace and shared
> fences, decreases ability to debug things.
>
> Ideally we wouldn't offer users known untested/broken scenarios, so
> yes we'd prefer that drivers that intend to expose a userspace fencing
> api around dma-fence would adhere to the rules of the gpu drivers.
>
> I'm not say you have to drop using dma-fence, but if you move towards
> cross-device stuff I believe other drivers would be correct in
> refusing to interact with fences from here.
The flip side is if you only used dma-fence.c "because it's there",
and not because it comes with an uapi attached and a cross-driver
kernel internal contract for how to interact with gpu drivers, then
there's really not much point in using it. It's a custom-rolled
wait_queue/event thing, that's all. Without the gpu uapi and gpu
cross-driver contract it would be much cleaner to just use wait_queue
directly, and that's a construct all kernel developers understand, not
just gpu folks. From a quick look at least habanalabs doesn't use any
of these uapi/cross-driver/gpu bits.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
next prev parent reply other threads:[~2020-05-12 6:12 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-11 9:11 [PATCH 1/3] drm/writeback: don't set fence->ops to default Daniel Vetter
2020-05-11 9:11 ` [PATCH 2/3] dma-fence: use default wait function for mock fences Daniel Vetter
2020-05-11 9:41 ` Chris Wilson
2020-05-11 10:12 ` Daniel Vetter
2020-05-11 18:13 ` [Intel-gfx] " Ruhl, Michael J
2020-05-11 18:17 ` Ruhl, Michael J
2020-05-11 9:11 ` [PATCH 3/3] misc/habalabs: don't set default fence_ops->wait Daniel Vetter
2020-05-11 9:36 ` Oded Gabbay
2020-05-11 9:43 ` Oded Gabbay
2020-05-12 2:14 ` [Intel-gfx] " Dave Airlie
2020-05-12 6:12 ` Daniel Vetter [this message]
2020-05-14 11:38 ` Oded Gabbay
2020-05-20 18:04 ` Daniel Vetter
2020-05-20 18:09 ` Oded Gabbay
2020-05-11 18:12 ` [PATCH 1/3] drm/writeback: don't set fence->ops to default Ruhl, Michael J
2020-05-20 18:03 ` Daniel Vetter
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